Transistors, such as field effect transistors (FETs), having high breakdown voltages (e.g., above about 15 to about 80 volts or greater) are used in various applications, such as power management or amplification and for driver systems. For example, the breakdown voltage may be defined as the voltage at which the drain (or source) breaks down while the transistor is turned off. In addition, transistors having high breakdown voltages may be used on the periphery of a memory device. For example, these transistors can be located between charge pumps and the string drivers of a memory device that provide voltages to the access lines (e.g., word lines) and can be used in charge pump circuitry and for the string drivers.
One technique for creating transistors with high breakdown voltages uses a lightly doped region between a source/drain region and the control gate of the transistor. This region is sometimes referred to as a drain extension region.
Aside from device geometry, breakdown voltage of such transistors can be dependent upon doping levels between the source/drain region and the control gate. This region between the source/drain region and the control gate is sometimes conductively doped at the same time as doping of the source/drain region itself because doping these regions separately add process steps and thus fabrication costs. However, doping levels desirable for contacts to the source/drain region may not lead to desirable breakdown voltages.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative transistor structures.